This invention is related to multi-speed power transmission utilized in powertrains and capable of providing at least six forward speed ratios and one reverse speed ratio from three planetary gearsets and five torque-transmitting mechanisms.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier patent employs three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in Lepelletier is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of the present to provide an improved family of multi-speed power transmission mechanisms having three planetary gearsets.
In one aspect of the present invention, the power transmission has three planetary gearsets each with three rotatable members.
In another aspect of the present invention, the three rotatable members are comprised of a sun gear member, a ring gear member, and a planet carrier assembly member.
In yet another aspect of the present invention, a first member of the first planetary gearset is continuously connected with a first member of the second planetary gearset, a second member of the second planetary gearset is continuously connected with a first member of the third planetary gearset, and a third member of the second planetary gearset is continuously connected with a stationary portion of the transmission, such as a housing.
In still another aspect of the present invention, an input shaft is connected with a member of one of the planetary gearsets and an output shaft is connected with another member of one of the planetary gearsets.
In yet still another aspect of the present invention, each family member has five torque-transmitting mechanisms comprised of three rotating type torque-transmitting mechanisms and two stationary type torque-transmitting mechanisms in a plurality of the family members, and comprising four rotating type torque-transmitting mechanisms and one stationary type torque-transrmitting mechanism in a plurality of other members of the family.
In still another aspect of the present invention, a first of the torque-transmitting mechanisms selectively interconnects a member of the first planetary gearset with the input shaft, output shaft, one of the interconnecting members, or a member of the second or third planetary gearset.
In yet still another aspect of the present invention, a second of the torque-transmitting mechanisms selectively interconnects a member of the second planetary gearset with the input shaft, output shaft, one of the interconnecting members, or a member of the first or third planetary gearset.
In yet still another aspect of the present invention, a third of the torque-transmitting mechanisms selectively interconnects a member of the third planetary gearset with either the input shaft, the output shaft, one of the interconnecting members, or a member of the first or second planetary gearset.
In a further aspect of the present invention, a fourth of the torque-transmitting mechanisms either selectively connects a member of the first, second or third planetary gearset with another member of one of the planetary gearsets, or operates as a stationary torque-transmitting mechanism to selectively connect a member of the first or third planetary gearset with a stationary member of the transmission.
It is a yet further aspect of the present invention wherein a fifth of the torque-transmitting mechanisms selectively connects a member of one of the planetary gearsets with a stationary member of the transmission.
In yet still a further aspect of the present invention, the five torque-transmitting mechanisms are selectively engaged in combinations of two to yield at least six forward speed ratios and one reverse speed ratio between the input shaft and the output shaft of the transmission.
The present invention is defined in a family of transmissions incorporating a plurality of family members. Each family member includes three planetary gearsets and five torque-transmitting mechanisms. The first and second of the planetary gearsets are continuously interconnected with an interconnecting member between the first members of each planetary gearset. The second and third planetary gearsets are continuously interconnected with an interconnecting member between a second member of the second planetary gearset and a first member of the third planetary gearset. The third member of the second planetary gearset is continuously connected with a transmission housing. Therefore, the second planetary gearset does not include any non-continuously interconnected planetary members.
An input shaft is continuously connected with at least one member of the first or third of the planetary gearsets and an output shaft is continuously connected with another of the members of the first or third planetary gearsets. When the input shaft is connected with the first planetary gearset and the output shaft is connected with the third planetary gearset, each of these planetary gearsets have one member that is non-continuously interconnected. When both the input shaft and the output shaft are continuously connected with members of the same planetary gearset, then the other of the first or third planetary gearsets has two normally non-continuously interconnected members.
The five torque-transmitting mechanisms are selectively engageable to provide selective interconnections between the normally non-connected planetary members with either other normally non-connected planetary members, with a transmission housing, or with each other. The five torque-transmitting mechanisms comprise three clutches and two brakes in a plurality of the family members, and comprise four clutches and one brake in another plurality of the family members. In all of the family members, the five torque-transmitting mechanisms are engaged in combinations of two to establish at least six forward speed ratios and one reverse speed ratio between the input shaft and the output shaft.
In some of the family members, it is possible to provide seven forward speeds through the judicious selection of the torque-transmitting mechanisms in combinations of two. Each of the members of the planetary gearsets comprises either a sun gear member, a ring gear member, or a planet carrier assembly member. The planet carrier assembly member may be of the single pinion type, that is a single mesh between the sun gear member and the ring gear member, or of the double pinion type, that is a plurality of intermeshing pinion pairs, one meshing with the sun gear member and the other meshing with the ring gear member. Both types of these planetary gearset styles are well known.
The numerical value of these speed ratios, which are available or otherwise provided between the input shaft and the output shaft, are determined utilizing the ring gear/sun gear tooth ratios of the planetary gearsets. Since the five torque-transmitting mechanisms permit a variety of selective interconnections between the planetary gearsets, it is possible that the individual numerical values of the gear ratios will utilize more than one of the planetary gearsets, and in many cases, two or more of the speed ratios will utilize the same ring gear/sun gear tooth ratios. For example, the reverse speed ratio, the first forward speed ratio, and the fifth forward speed ratio might all utilize the ring gear/sun gear tooth ratios of all three of the planetary gearsets. However, in each of these ratios, the combination of torque-transmitting mechanisms provides different power paths through the planetary gearsets and therefore different numerical values for the speed ratios. This will be evident from the family members that are described below.